BANGALORE, March 16 (Reuters) - United Therapeutics Corp (UTHR.O) said the approval for its inhaled drug to treat pulmonary hypertension could be delayed as it would have to conduct an additional study after the U.S. health regulators raised certain questions.

The U.S. Food and Drug Administration had questions regarding human factors testing and the instructions for use of the portable nebulizer that delivers the drug.

Analysts, however, do not see the additional study as a major roadblock and expect the approval of the drug, Tyvaso, to be pushed back by about six months.

“Instructions-for-use studies are among the most minor in terms of severity for device amendments,” Leerink Swann analyst Joseph Schwartz said. He now expects the drug to be launched between mid-2009 and the first quarter of 2010.

United Therapeutics said it agreed to conduct human factors testing to validate that the revised instructions for use, which it had provided the FDA, results in the proper use of the device by a naive user.

In a conference call with analysts, the company said it expects to complete the study in about a month’s time. The FDA currently has an action date of April 30 on the drug.

“We hope that any delay related to this issue will be limited to just a few months,” Chief Executive Martine Rothblatt added.

However, Collins Stewart analyst Salveen Kochnover said she expects the finalization of the study protocol, patient recruitment, study completion and data evaluation to take more than six weeks.

“It does not seem like an overwhelming issue. It is really about making sure that patients can use the device safely and efficaciously,” she added.

Kochnover, who sees an approval for Tyvaso coming in the fourth quarter, expects sales of $2.5 million in that quarter and $51.4 million in 2010.

Shares of the Silver Spring, Maryland-based company were trading down more than 9 percent at $60 Monday afternoon on Nasdaq. They had earlier hit a low of $59.35.

BUYING OPPURTUNITY?

The sell-off in United Therapeutics shares could, however, prove to be a good entry point as the company is all set to benefit from its U.S. marketing rights to Eli Lilly and Co’s (LLY.N) tadalafil — which is expected to get approved for the treatment of pulmonary arterial hypertension in May.

Tadalafil, which is already approved for the treatment of erectile dysfunction under the brand name Cialis, “carries much less risk for delay than Tyvaso, given the lack of device-related risk and an active ingredient already widely used in erectile dysfunction,” Leerink’s Schwartz said in a note. (Editing by Himani Sarkar)